Field of the Invention
The present invention relates to a hybrid vehicle, and particularly to a hybrid vehicle including an internal combustion engine, a power storage device, and an electric motor that receives electric power from the power storage device to generate vehicle driving force.
Description of the Background Art
In the hybrid vehicle as described above, a driver may feel strangeness with acceleration because the vehicle speed and the rotation speed of the internal combustion engine are increased not in a proportionally-cooperative manner during acceleration. In order to solve such a problem, for example, Japanese Patent Laying-Open No. 2009-210045 discloses that, during acceleration of a vehicle, the target rotation speed of the internal combustion engine is set such that the sound pressure of the internal combustion engine is proportionally increased relative to the vehicle speed increase.
When performing rotation speed control of the internal combustion engine disclosed in Japanese Patent Laying-Open No. 2009-210045, the target rotation speed of the internal combustion engine is set such that the sound pressure of the internal combustion engine is proportionally increased relative to the vehicle speed increase, which causes shortage of traveling power, which is replenished by means of an electric motor that receives electric power from the power storage device to generate vehicle driving force. When the power replenished by means of the electric motor during execution of rotation speed control of the internal combustion engine is permitted up to a relatively large value, the flexibility to set the rotation speed of the internal combustion engine is increased, thereby increasing the possibility that a desired sound pressure increase (rotation speed increase) can be realized. However, the operating point of the internal combustion engine greatly deviates from a region in which the internal combustion engine efficiently operates, so that the fuel efficiency of the internal combustion engine may deteriorate.
However, in the case where the rotation speed control of the internal combustion engine as described above is applied to a hybrid vehicle that can travel while selecting one of a CD (Charge Depleting) mode and a CS (Charge Sustaining) mode, there may be room for improvement in fuel efficiency, which is however not particularly taken into consideration in Japanese Patent Laying-Open No. 2009-210045.